Combination vacuum and over-pressure process chamber and methods related thereto

ABSTRACT

A process chamber system adapted for both vacuum process steps and steps at pressures higher than atmospheric pressure. The chamber door may utilize a double door seal which allows for high vacuum in the gap between the seals such that the sealing force provided by the high vacuum in the seal gap is higher than the opposing forces due to the pressure inside the chamber and the weight of the components.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/919,169 to Moffat et al., filed Mar. 12, 2018 which claims priorityto U.S. Provisional Patent Application No. 62/469,522 to Moffat et al.,filed Mar. 10, 2017, which are hereby incorporated by reference in theirentirety.

FIELD OF THE INVENTION

This invention relates to process chambers, namely a process chamberadapted for both vacuum and pressure processes.

BACKGROUND

What is called for is a process chamber system that allows for bothvacuum processing and processing in pressures greater that atmosphericpressure in the same chamber.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial cutaway view of a process chamber system accordingto some embodiments of the present invention.

FIG. 2 is a bottom view through a cut line of a process chamber systemaccording to some embodiments of the present invention.

FIG. 3 is a bottom view of a process chamber according to someembodiments of the present invention.

FIG. 4 is a static seal compression chart.

FIG. 5 is a chart showing the static seal compression vs. thecompression load per seal linear inch.

SUMMARY

A process chamber system adapted for both vacuum process steps and stepsat pressures higher than atmospheric pressure. The chamber door mayutilize a double door seal which allows for high vacuum in the gapbetween the seals such that the sealing force provided by the highvacuum in the seal gap is higher than the opposing forces due to thepressure inside the chamber and the weight of the components.

DETAILED DESCRIPTION

In some embodiments of the present invention, as seen in FIG. 1, acombination process chamber system 100 is seen with its chamber 103 andchamber opening flange 101. The chamber has its opening facing downwardand is adapted to receive wafers 104 from below. The chamber door 102 israised from underneath with a door lift mechanism 105, which may be ahydraulic mechanism. The wafers may lay horizontally and be stackedvertically in a cart or other stacking holder. The top surface 112 ofthe chamber door 102 may have grooves for an inner O-ring and an outerO-ring with a mating outline for these grooves seen on the bottom matingsurface of the chamber opening flange 101.

FIG. 2 illustrates the view looking upward into the chamber 103 frombelow. The bottom of the chamber 103 is rimmed with a flange 101 adaptedto mate with a top surface 112 of the chamber door 102. The flange 101has grooves for an inner O-ring and an outer O-ring with a matingoutline for these grooves seen on the top mating surface of the chamberdoor 102. In some aspects, both O-ring grooves may be circular. In someaspects, the O-ring grooves may be partially circular and may conform toother features of the surfaces upon which they reside. In some aspects,the O-ring grooves may be of another shape. The flange 101 has an innerseal O-ring 107 and an outer seal O-ring 106. A seal gap 108 occursbetween the inner seal 107 and the outer seal 106. A high vacuum source109 is coupled to the seal gap 108 via a high vacuum port 114.

The chamber is adapted to run at low pressures as well as pressurehigher than one atmosphere. A low vacuum port 110 is adapted to evacuatethe chamber. Also, a gas manifold 113 is adapted to provide gasses tothe chamber, including high purity dry inert gas. In some aspects, thechamber runs a low pressure process, such as drying a polyimideprecursor, for example. As discussed further below, the pressure duringsuch a process may be in the range of 1-15 Torr. As also discussedfurther below, in some processes low vacuum is alternated with highpurity inert gas to drive oxygen levels very, very, low. The gasmanifold 113 may provide gas through one or more gas ports into thechamber for such a process. In a low vacuum process, the door 102 may beraised up to the chamber 103 using the door mechanism 105. The chambersealing is done by the pull of the vacuum in the chamber across the areaof the door, pulling the door onto the O ring seals, providing the seal.

In some processes, it may be desired to also include an overpressurestep, for example, in the range of 1.1 to 1.2 atmospheres, including upto 910 Torr. This same process chamber system 100 may be used foroverpressure steps without having to transfer the treated substrates toa different chamber, and also without having to expose the substrates tooxygen, especially in the case where oxygen levels have beenpurposefully very low. Keeping the substrates in the same, sealed,chamber when alternating from vacuum to overpressure processes may allowfor the maintenance of an atmosphere that has had a target gas, such asoxygen, at very low levels. In contrast to purging a chamber, such aswith nitrogen, in order to remove oxygen, the use of vacuum pulls mayreduce the oxygen level to a parts per million range, as describedbelow. Further, the use of vacuum pulls alternated with pure dehydratedinert gas, as described below, may significantly reduce the oxygen levelto a lower level than other known processes may achieve, and then allowutilization of this low oxygen condition in an overpressure processstep.

In some aspects, the door mechanism 105 provides vertical lift to thechamber door 102 in order to allow the top surface 102 of the chamberdoor 102 to mate to the bottom surface of the chamber opening flange 101of the chamber 103. As described above, this mating of the chamber doorto the chamber opening flange may be the compression of an inner O-ringand an outer O-ring. In some aspects, the sealing force provided by thedoor mechanism 105 is added to the sealing force provided by evacuatingthe seal gap 108 to determine the total sealing force available. Thechamber pressure on the door provides a counter force, as do the weightof the door and the cart components, as well as the O-ring sealcompression spring force. In some aspects, the sealing force provided bythe door mechanism and the evacuated seal gap area are gauged to provideenough sealing force to keep the chamber door sealed during anoverpressure process in the process chamber without any other sealingclamp or fastening mechanisms. In the case of a process chamber isolatedfrom direct user contact and instead confined to an area wherein wafersare moved in and out of the process chamber using robots, having aprocess chamber which can withstand an overpressure process step withoutexternal latching allows for such a use.

In an exemplary process according to some embodiments of the presentinvention, a polyimide precursor is applied to a silicon substrate. Insome aspects, the polyimide precursor is applied directly over thesilicon substrate. In some aspects, the polyimide precursor is appliedover other layers already on a substrate, which may be other polyimidelayers and metal layers, for example. In some aspects, the solvent usedin the polyimide precursor is NMP. An expected thickness forsemiconductor applications is in the range of 7-10 microns. Although asingle substrate could be processed, in some aspects a plurality ofsubstrates may be processed. As seen, a process oven may be used tosupport a plurality of substrates within a chamber. The process oven mayinclude internal heaters, heated inert gas inputs, and vacuumcapability. The substrates are placed into the chamber that has beenheated to 150 C. In some aspects, the chamber is heated to a temperaturein the range of 135 C to 180 C. The chamber pressure is reduced to afirst drying pressure of 50 Torr. In some embodiments, the first dryingpressure is in the range of 30-60 Torr. After reaching the first dryingpressure, the chamber may then be flushed with a heated inert gas suchas nitrogen at a pressure of 600 Torr. In some aspects the heated inertgas may be at a pressure in the range of 550 to 760 Torr. The nitrogenmay be heated to the same temperature as the chamber, 150 C. The chamberpressure is then reduced to a second drying pressure of 25 Torr. In someembodiments, the second drying pressure is in the range of 15-30 Torr.After reaching the second drying pressure, the chamber may then beflushed with a heated inert gas such as nitrogen at a pressure of 600Torr. In some aspects the heated inert gas may be at a pressure in therange of 550 to 760 Torr. The nitrogen may be heated to the sametemperature as the chamber, 150 C. The chamber pressure is then reducedto a third drying temperature of 1 Torr. In some embodiments, the thirddrying pressure is in the range of 1-15 Torr. After reaching the thirddrying pressure, the chamber may then be filled with heated inert gas,such as nitrogen, up to 650 Torr, in preparation for imidization of thepolyimide precursor. The substrates may then undergo temperatureimidization in the same chamber. As described further below, the oxygenlevel in the process oven may now be very extremely low. The subsequenttemperature imidization may occur at 350-375 C, and as further describedbelow.

In an exemplary embodiment further illustrating the timing of a processas described above, a process may begin with the heating of the processoven to a temperature of 150 C. A single substrate or a plurality ofsubstrates within the process oven, which include a polyimide precursorincluding a solvent such as NMP, are put into the process oven which hasbeen preheated to the temperature of 150 C. The process oven pressure isthen reduced to a first drying pressure of 50 Torr. This portion of theprocess may take 2-3 minutes. The process oven is then flushed withpreheated nitrogen heated to 150 C up to a pressure of 600 Torr. Thisportion of the process may take 2-3 minutes. The process oven pressureis then reduced to a second drying pressure of 25 Torr. This portion ofthe process may take 3-4 minutes. The process oven is then flushed withpreheated nitrogen heated to 150 C up to a pressure of 600 Torr. Thisportion of the process may take 2-3 minutes. The process oven pressureis then reduced to a third drying pressure of 1 Torr. This portion ofthe process may take 4-5 minutes. The process oven is then flushed withpreheated nitrogen heated to 150 C up to a pressure of 650 Torr. Thisportion of the process may take 2-3 minutes. The aforementioned stepshave now greatly reduced the oxygen level in the process oven, as wellas having removed all or nearly all of the solvent from the polyimideprecursor with little or no bubbling or skinning of the polyimideprecursor.

The oxygen level in the process oven may now be down as low asapproximately 1 ppm, as an end result of the drying process. The vacuumpulsing as described above, in conjunction with the intervening flushingwith nitrogen, provides a benefit for a subsequent imidization process,which is already separately enhanced by the significantly enhanceddrying. The vacuum pulsing and intervening flushing results in a muchlower oxygen level in the process chamber as the substrates go furtherin the process. In contrast to prior methods which pull vacuum once fora combined drying/imidization process, the vacuum pulsing reduces thepartial pressure of oxygen significantly, as each flushing with nitrogenresets the initial gas balance prior to the next pull of vacuum. Theinflows of heated inert gas enhance the heating of the polyimideprecursor layer, as well as the fixturing within the chamber and thechamber itself. The reduced pressure of the process described hereinenhances, and speeds up, the evaporation of the solvent, and also allowsfor a temperature to be used for the evaporation that is below theskinning temperature of the polyimide precursor. The staging of thereduced pressure at sequentially lower pressures reduces bubbling whichmight occur by simply going straight to a much reduced pressure, andavoids the residual solvent which would remain if the very reducedpressure is not utilized. Residual solvent may inhibit the imidizationof the polyimide precursor. The pulsing and flushing then further addsthe benefit of a final chamber composition with significantly lessoxygen than prior methods, reducing or eliminating the browning whichmay occur in the polyimide layer during temperature imidization in thepresence of oxygen.

With the tiered vacuum application, in conjunction with nitrogenflushing, oxygen levels may be driven very, very low. With theabove-described process, the starting concentration of oxygen at theinitial atmospheric conditions is approximately 230,000 parts permillion (ppm). When the initial vacuum is applied down to 50 Torr, andthen the chamber is refilled with nitrogen, the concentration of oxygenwill have been reduced to approximately 15,131 ppm. With the subsequentvacuum pull down to 25 Torr, and then refilling with nitrogen, theconcentration of oxygen will have been reduced to approximately 498 ppm.With the final vacuum pull down to 1 Torr, and subsequent refilling withnitrogen, the resulting concentration of oxygen will be down to 0.65ppm. The very, very, low oxygen concentrations that result allow for asubsequent processing, including temperature imidization, at oxygenconcentrations well below any prior process. In actual practice, thepurity of the nitrogen supply may become the active parameter in how lowof an oxygen concentration can be reached. If the nitrogen supply isknown to have 10 ppm oxygen, for example, then that will limit the depthof oxygen removal. Some processing chambers may have nitrogenavailability with down to 1 ppm O2, and with such a system oxygenconcentration can be driven down to approximately 1 ppm. Simple flushingof a chamber with pure nitrogen provides some reduction in oxygenconcentration, but such processes are very time consuming and do notachieve results at all comparable to the above-described process.

Further, the use of heated nitrogen for the re-filling steps in theabove-described process works to minimize the effects of freezing thanmay have happened during the vacuum pull. As water boils at 72 C at 50Torr, 26 C at 25 Torr, and −21 C at 1 Torr, the heated nitrogen inputthus facilitated evaporation of any water than may be found in thedevices being dried or outgassed.

In some aspects, a process that began using steps utilizing low vacuummay also then want to include a step that is at a pressure greater thanatmospheric pressure. The step using pressure greater than atmosphericpressure may include heating of the substrates. For this step, the highvacuum port coupled to the seal gap is driven to near absolute vacuum.The force due to the overpressure situation in the chamber, which is thepressure times the area within the inner seal, must be overcome by thehard vacuum in the seal gap as applied across the area within the sealgap.

A discussion of the forces involved is seen here:

Applied Load Factors

${\sum\limits_{1}^{N}E} = {{{F\mspace{14mu}{Chamber}\mspace{14mu}{Pressure}} + {F\mspace{14mu}{Door}\mspace{14mu}{Cart}\mspace{14mu}{Components}\mspace{14mu}{Weight}} + {F\mspace{14mu}{Static}\mspace{14mu}{Seal}\mspace{14mu}{Compression}} - {F\mspace{14mu}{Door}\mspace{14mu}{Cart}\mspace{14mu}{Lift}\mspace{14mu}{Capacity}}}<={F\mspace{14mu}{Vacuum}\mspace{14mu}{Hold}\mspace{14mu}{Capacity}}}$

The chamber sealing force must overcome the weight of the door and thecomponents on the cart which is raised with the door. Also, the chambersealing force must overcome the force due to the chamber pressureexerting downward across the horizontal area out to the inner O-ring.The chamber sealing force must also overcome the force generated by thecompression of the O-ring seals (the static sealing compression). Thecomponents contributing to the chamber sealing force are the door liftmechanism force, and the vacuum hold force of the vacuum across the areabetween the O-rings.

The static seal compression depends upon a variety of factors. The ShoreA Hardness of the O-ring seals, the diameter of the O-rings, and thetotal length of the two O-rings are among the factors. A softer O-ringcan seal at a lower pressure, and an O-ring with a larger diameter mayoffer a better seal in the case of imperfections in the flanges,including some lack of flatness. However, most if not all O-rings over0.250 inches in diameter are spliced, and this may lead to otherproblems. In an exemplary embodiment, the O-rings are 0.250 inches indiameter and of a 50 durometer Shore A Hardness.

A static seal compression chart for basic O-ring elastomers is seen inFIG. 4.

The above chart shows great variance of what the true static seal loadrequirements should be.

${\%\mspace{14mu}{Compression}} = {\frac{.043}{.275} = {15.5\%}}$

We will use 15% for calculation. Since 15% is in between data for 10%and 20%, we will use the mean value for both 50 durometer data sets andaverage the results.

Using exemplary inner and outer diameters as 19.75 and 21.25 inches,respectively, as a starting point, we see:Mean Averaged Compression Load=10 lbs/inF Static Seal Compression=Mean Averaged Compression Load×SealCircumference TotalCtotal=Ci+Co=π(di+do)do=21.25 indi=19.75 inCtotal=π(19.75+21.25)=128.8 inFStatic Seal Compression=10×128.8=+1288 lbs

The chart in FIG. 5 shows the static seal compresCsion vs compressionload per seal linear inch, throughout the entire chart range.

In an exemplary embodiment, a cart lift system has two pneumatic liftingcylinders capable of 145 psig, with 40 mm cylinder diameters.

${F\mspace{14mu}{Cart}\mspace{14mu}{Lift}\mspace{14mu}{Capacity}} = {{2\;{PA}} = \frac{(2)145\;\pi\; d^{2}}{4}}$d = 40/(25.4) = 1.575  in F  Cart  Lift  Capacity = −565  lbs

Using the calculation from page one, the required vacuum lift capacitycan be determined.

$\;{{\sum\limits_{1}^{N}E} = {{{F\mspace{14mu}{Chamber}\mspace{14mu}{Pressure}} + {F\mspace{14mu}{Door}\mspace{14mu}{Cart}\mspace{14mu}{Components}\mspace{14mu}{Weight}} + {F\mspace{14mu}{Static}\mspace{14mu}{Seal}\mspace{14mu}{Compression}} - {F\mspace{14mu}{Door}\mspace{14mu}{Cart}\mspace{14mu}{Lift}\mspace{14mu}{Capacity}}}<={F\mspace{14mu}{Vacuum}\mspace{14mu}{Hold}\mspace{14mu}{Capacity}}}}$  354 + 358 + 1288 − 565 ≤ F  Vacuum  Hold  Capacity  1435  lbs ≤ F  Vacuum  Hold  Capacity

As seen, the seal compression loads tend to dominate this calculation.

The gap area between the seals is designed to be sufficiently large toprovide the force needed to seal, in concert with the above analysis.

For example, a 19.9 inch diameter inner seal and an outer seal in therange of 25.0 inch outer seal may provide the force needed to seal withthe above process parameters.

As evident from the above description, a wide variety of embodiments maybe configured from the description given herein and additionaladvantages and modifications will readily occur to those skilled in theart. The invention in its broader aspects is, therefore, not limited tothe specific details and illustrative examples shown and described.Accordingly, departures from such details may be made without departingfrom the spirit or scope of the applicant's general invention.

What is claimed is:
 1. A method for processing in a process chamber,said method comprising the steps of: loading substrates into a processchamber through a downward facing chamber door opening, said chambercomprising a chamber door opening flange around said chamber dooropening and a chamber door; closing the chamber door by raising thechamber door from underneath the process chamber door opening, whereinsaid chamber door comprises: a sealing surface adapted to seal to saidchamber door opening flange; an inner groove on said sealing surface; aninner O-ring residing in said inner groove; an outer groove on saidsealing surface; and an outer O-ring residing in said outer groove;creating a door seal between the chamber door sealing surface and thechamber door opening flange by pulling a vacuum between two seals whichcreate said door seal using a high vacuum source; running a firstprocess step in the process chamber while said process chamber is undervacuum; and running a second process step in the process chamber at apressure greater than atmospheric pressure.
 2. The method of claim 1wherein said first process step comprises a heating step.
 3. The methodof claim 1 wherein said method is a method for temperature imidizationof a polyimide precursor.
 4. The method of claim 1 wherein said secondprocess step comprises a heating step.
 5. The method of claim 1 whereinthe step of lifting the door up comprises lifting the door up with adoor lift mechanism with a known maximum lift capacity.
 6. The method ofclaim 5 wherein said chamber door and said chamber are not held closedwith a mechanical latch or fasteners other than the door lift mechanismand the force of vacuum between the two seals which create the doorseal.
 7. A method for processing in a process chamber, said methodcomprising the steps of: loading substrates into a process chamberthrough a downward facing chamber door opening, said chamber comprisinga chamber door opening flange around said chamber door opening and achamber door; closing the chamber door by raising the chamber door fromunderneath the process chamber door opening, wherein said chamber doorcomprises: a sealing surface adapted to seal to said chamber dooropening flange; an inner groove on said sealing surface; an inner O-ringresiding in said inner groove; an outer groove on said sealing surface;and an outer O-ring residing in said outer groove; creating a door sealbetween the chamber door sealing surface and the chamber door openingflange by pulling a vacuum between two seals which create said door sealusing a high vacuum source, wherein said method is a method fortemperature imidization of a polyimide precursor.